Device for concentrating the electron beam in a high-power klystron comprising more than two cavity resonators



March 2, 1965 w, SCHMlDT ETAL 3,172,008

DEVICE FOR CONCENTRATING THE ELECTRON BEAM IN A HIGH-POWER KLYSTRONCOMPRISING MORE THAILTWQ CAVITY RESONATORS Filed June 6, 1962 5Sheets-Sheet l FIGJ FIG.2

INVENTOR WOLFGANG SCHMIDT GERHARD SCHUMANN BY 5;; re.

AGENT March 2, 1965 w. SCHMIDT ETAL 3,172,008

DEVICE FOR CONCENTRATING THE ELECTRON BEAM IN A HIGH-POWER KLYSTRONCOMPRISING MORE THAN TWO CAVITY RESONATORS Filed June 6, 1962 5Sheets-Sheet 2 31 11 34 Bb 31 Ba 34 INVENTOR WOLFGANG scumor GERHARDSCHUMANN AGEN M r 1965 w. SCHMIDT ETAL' 3,172,003

DEVICE FOR CONCENTRATING THE ELECTRON BEAM IN A HIGH-POWER KLYSTRONCOMPRISING MORE THAN TWO CAVITY RESONATORS Filed June 6, 1962 5Sheets-Sheet 3 L0 S 9. 5 LL WOLFGANG SCHMIDT GERHARD SCHUMANN AGENTUnited States Patent C) DEVICE FOR CONCENTRATING THE ELECTRON 3 Claims.(a. 315-39 The invention relates to a device for concentrating theelectron beam of a high-power klystron having more than two cavityresonators, in with the magnetic fields, alternating their directions,are produced by means of permanent magnets with pole shoes contactingthe drift tube parts of the klystron.

Devices of the kind set forth are known and shown diagrammatically inFIG. 1. The alternating magnetic fields 3 travel between pole shoes 5and the permanent magnets are designated by 7. The direction of movementof the electron beam is denoted by 1. With highpower klystrons havingmore than two cavity resonators, which usually operate on comparativelylow frequencies, such a structure brings about, however, inconvenientdimensions and weights, not only of the assembly as a whole but also ofthe component parts, since in this case the large resonators must bebridged by the soft-iron yokes between the pole shoes 5 and the magnets7.

With low-power two-cavity klystrons it is known to arrange, between thetwo cavities, a short, single lens, which is excited by anelectro-magnet; this may, however, also be a permanent magnet. With aklystron having more than two cavity resonators the arrangement showndiagrammatically in FIG. 2 would be obtained, in which, like in FIG. 1,1 designates the direction of travel of the electron beam and 5 the poleshoes. The walls of the drift tube are designated by 11 and the magneticrings by 13, which produce magnet fields indicated by arrows between thepole shoes 5. However, this arrangement cannot be used in those cases inwhich the walls of the drift tube must be cooled by air, since thisrequires cooling vanes of a fairly large diameter with the associatedcold-air pipes. A further great disadvantage of such a concentration bymeans of magnetic single lenses would be that just in the region of theinductance gaps and modulation gaps 15 of the cavity resonators 17 thediameter of the electron beam has a minimum, which will be seen from thedrawing by the cross-hatched section of the electron beam. Because ofthe small beam diameter a heavy coupling between the electron beam andthe cavity resonators would not be possible. This is, howeverypossible,if the diameter of the electron beam approaches more closely that of theinteraction gap.

In a device for concentrating the electron beam in a high-power klystronhaving more than two cavity resonators, in which the magnetic fields ofalternating directions are produced by means of permanent magnets,having pole shoes contacting the parts of the drift tube of theklystron, the permanent magnets are arranged, in accordance with theinvention, at a given distance from the Walls of the drift tube outsidethe cooling members and are connected by magnetic yokes with the poleshoes, which extend on either side of the yokes in an axial directionover a distance such that axial magnetic fields are produced also in thespaces inside the cavity resonators, which fields have the oppositedirection as compared with those of the drift tube parts and haveapproximately the same intensity. With the structure according to theinice vention a periodic, axial magnetic field is obtained throughoutthe length of the klystron without the need for bridging the cavityresonators by magnetic yokes. With this arrangement the electron beammay, moreover, have a maximum diameter in the interaction space insidethe cavity resonators, so that a heavy coupling between the beam and thecavity resonators is possible.

A simple control of the magnetic field intensity may be obtained whenthe magnets consist of magnetic columns composed of parts, which arerelatively slidable, so that a more or less strong leakage field can beadjusted.

If sintered, oxidic permanent magnets are employed, the two pole shoesmay be at different potentials, which is advantageous with certaintubes.

In accordance with the invention the magnetic columns may be connectedwith the yokes, which are fastened by means of bolts or the like to thepole shoes.

The arrangement according to the invention, when sintered, oxidicmagnets are employed, consists in that the influence of temperature ofthe air-cooled parts on the magnets is only slight, so that from thisside the magnetic field is little affected by temperature.

The invention will now be described more fully with reference to FIGS. 3to 5, of which FIG. 3 shows diagrammatically a longitudinal sectionalview of a device according to the invention.

FIG. 4 is a plan view and FIG. 5 is a cross sectional view.

As is shown in FIG. 3 resonators 17 are arranged between the parts 11 ofthe drift tube. The parts 11 of the drift tube are provided with coolingvanes 19. In FIG. 5 the direction of travel of the cooling air isindicated by arrows 20. Between the outer vane 21 and the walls 23 ofthe resonators there are arranged pole shoes 25, which are connected viasoft-iron yokes 27, with the magnetic columns 29, showndiagrammatically. These columns 29 are disposed towards the outer sideto an extent such that they do not hinder the cooling operation. Thecolumns 29 consist of stacked, oxidic magnets.

Inside the drift tube parts 11, in the regions 31, magnetic fields B,,are produced in the direction of travel of the electron beam 1, if themagnetic columns 29 are all oriented in the same direction. However,magnetic fields B in opposite direction are produced at the same time inthe high-frequency interaction spaces 34 away from the pole shoes 25.Because of the periodic magnetic field along the electron beam 1 thevariations in diameter of the beam are considerably smaller than in thearrangement of FIG. 2; in the regions 34 the electron beam hasapproximately its maximum diameter, so that a fixed coupling with thecavity resonators is possible. The same intensity of the magnetic fieldsB and B is obtained by the choice of the pole shoe parts c and d oneither side of the yokes 27, so that the lengths a and b of the magneticfield portions in the drift tube and in the cavity resonatorrespectively can be adjusted.

From FIGS. 4 and 5 it will be seen that the magnetic yokes compriseparts 37, which are connected with the pole shoes 25, and parts 43,between which parts the magnetic columns are arranged, which areprovided with flanges 39 and 41 respectively of non-magnetic material.The magnetic columns consist of two discs 45, glued to the yoke parts 43and having arranged between them a disc 47, which is slidable alongguide rods 49. To this end connecting rods 50, provided with screwthreads, are coupled with screw-threaded bars 51, which can be turned bymeans of a hand-wheel 53. The two halves of the screw-threaded bar 51are intercoupled at 55. By displacing the discs 47 by turning thescrew-threaded bar 51, the intensity of the magnetic field can beadjusted.

The device according to the invention may be employed with klystronshaving a resonator diameter of 100 cms.; in the case of four resonatorsthe overall length is 180 cms.

What is claimed is: 1. A device for concentrating an electron beam in adrift tube of a klystron having atleast three cavity, resonatorscomprising means to cool the drift tube, means for producing magneticfields in the drift tube alternating in direction between the cavityresonators, said magnetic field producing means including permanentmagnets posia tioned' beyond the cooling means and spaced" from thedrift tube, pole-pieces adjacent to portions of the drift tube betweensuccessive cavity resonators, and a yoke of magnetic material connectingeach magnet with. a pole piece, each of said pole-pieces extending inthe direction of the drift tube on either side of the yoke adi'stan'ceat which an axial magnetic field is. produced in the adjacent cavityresonator having approximately a direction opposite to and having thesame intensity as that produced in the adjacent section of the drifttube.

2. A device as claimed in claim 1 in which the magnets are constitutedof columns having parts displaceable relative to one another. g

3. A device as claimed in claim2 in which the columns are connected withthe yokes and the yokes are secured 2,837,686 Drieschmanetal June 3,1958 2,940,000 Geisler June 7, 1960 2,993,141 Post July 18, 1961

1. A DEVICE FOR CONCENTRATING AN ELECTRON BEAM IN A DRIFT TUBE OF AKLYSTRON HAVING AT LEAST THREE CAVITY RESONATORS COMPRISING MEANS TOCOOL THE DRIFT TUBE, MEANS FOR PRODUCING MAGNETIC FIELDS IN THT DRIFTTUBE ALTERNATING IN DIRECTION BETWEEN THE CAVITY RESONATORS, SAIDMAGNETIC FIELD PRODUCING MEANS INCLUDING PARMANENT MAGNETS POSITIONEDBEYOND THE COOLING MEANS AND SPACED FROM THE DRIFT TUBE, POLE-PIECESADJACENT TO PORTIONS OF THE DRIFT TUBE BETWEEN SUCCESSIVE CAVITYRESONATORS, AND A YOKE OF MAGNETIC MATERIAL CONNECTING EACH MAGNET WITHA POLEPIECE, EACH OF SAID POLE-PIECES EXTENDING IN THE DIRECTION OF THEDRIFT TUBE ON EITHER SIDE OF THE YOKE A DISTANCE AT WHICH